Also thank you to everyone that have shared their opinions, it's truly priceless, and I appreciate every single post.

So I'm now looking at 325i at an older plate around the 14k mark.

But in the meantime I will go to see the 320i, I will see how it drives and just generally see how it is, and whether the seller would drop his price below the £13k mark. Also see if he is willing to chuck in a BMW warranty for the year.